1. The Field of the Invention
The present invention is related to apparatus and methods for measuring a workpiece in a workpiece holder of a numerically controlled lathe. More particularly, the present invention is related to a multiple stylus probe attachment for attachment to a probing mechanism mounted in a turret tool station of a numerically controlled lathe and used for probing various surfaces of a workpiece.
2. Technical Background
The incorporation of electronic inspection probes in numerically controlled lathes permits the rapid, precise inspection of the workpiece, while reducing to a minimum the possibility for operator error. Through the use of such probes, scrap levels are reduced and efficiency is greatly enhanced.
A typical inspection probe utilized in a numerically controlled lathe includes a probing mechanism which is mounted in one of the turret tool stations of the lathe. Attached to and extending outwardly from the probing mechanism is a stylus having a sensing tip such as a ruby ball. Within the probing mechanism is an electronic switch which is actuated when the sensing tip of the stylus comes into contact with the part being measured.
Once the probe has been calibrated, the probe may be used in a variety of ways to expedite the machining of workpieces and to increase the efficiency and accuracy of the machining process. For example, the probe may be used to calibrate tools and to monitor tool wear. Additionally, the probe may be used to check workpieces prior to their removal from the lathe to ensure that they have been machined within permitted tolerances.
Because workpieces may be required to be machined into a variety of configurations, it may be necessary to utilize different configurations of styli in order to permit the probe to reach the various surfaces. For example, on the workpiece 10 of FIG. 1, the stylus 12 is configured such that it may be used to probe a front face 14, a back face 16 and an outside diameter 18 of the workpiece 10. Because of the shape of the stylus 12, it cannot be used to probe the inside diameter 20.
To permit the probe to measure the inside diameter 20 of the workpiece, a different shaped stylus must be used. Thus, in conventional practice, the stylus 12 is removed from the probing mechanism and a different shaped stylus 22, such as that illustrated in FIG. 2, is attached. With the stylus 22 mounted on the probing mechanism, the outside diameter 18, the inside diameter 20 and the front face 14 of the workpiece 10 may be probed.
A principal disadvantage to replacing the stylus is the time required to recalibrate the probe for the new stylus. Calibration of the probe generally involves initially setting or "timing" the probe off a point having a known coordinate, such as a point on the chuck or fixture for which a Z coordinate (axially of the workpiece) is known. This coordinate value is entered into the computer which controls the lathe and this coordinate value serves as a starting point for calibration. The probe must also be timed to a point having a known X coordinate (radially of the workpiece).
Each of the tools on the lathe must then be timed to the points on the fixture to which the probe was timed. Depending on the lathe being used, there may be over a dozen tools which must be timed in this fashion. Timing the tools to the same known coordinates as the probe ensures that the tools are synchronized to the probe. Thus, as further adjustments are made to calibrate the probe, these adjustments will automatically be translated to the tools.
A test cut or check point is then cut into the workpiece with each tool. The check point is probed with the probe and the coordinate recorded. A micrometer may be used to manually measure the workpiece at the checkpoint. (The micrometer should first be checked against a standard to ensure that it is calibrated.) The result of the manual measurement with the micrometer is then compared with the measurement taken by the probe. The probe is then offset to compensate for any difference between the two measurements.
The machining program is then run and the workpiece is machined by the tools of the lathe according to the specifications programmed into the lathe. When the first workpiece is completed, a "first article inspection" is conducted by placing the completed workpiece on a coordinate measuring machine or other standardized measuring tool and measuring it to verify whether the manual measurement taken by the micrometer was accurate. If a discrepancy is found, the probe may be further offset, thereby completing the calibration process.
After the probe has been calibrated, numerous workpieces may be accurately machined by the lathe without having to further adjust the probe. Each workpiece may be probed, thereby monitoring tool wear and enabling the lathe operator to know when tools should be replaced. However, if a probe having a different shape of stylus is required to complete the machining of a workpiece or to machine a different part, the probe must be recalibrated with the new stylus by following the same procedure outlined above.
In many instances, the time-consuming procedure of switching probes and recalibrating, as described above, is the accepted procedure when machining workpieces requiring two configurations of probes for inspection. Calibrating a probe according to the procedure described above can result in a set-up time of greater than 45 minutes. Thus, each time a different stylus is mounted on the probe, substantial time must be invested in recalibrating the probe.
Thus, it would be an advancement in the art to provide probing apparatus and methods which would permit the measurement of various surfaces of a workpiece, thereby avoiding the need to repeatedly change the stylus and recalibrate the probe.
Indeed, it would be a further advancement in the art to provide apparatus and methods for probing a workpiece in a lathe, whereby different shaped styli could be employed in connection with a single probe, while avoiding having to repeatedly recalibrate the probe each time a different stylus is necessitated.
Such apparatus and methods are disclosed and claimed herein.